Beine Harry, Anastasio Cort, Esposito Giulio, Patten Kelley, Wilkening Elizabeth, Domine Florent, Voisin Didier, Barret Manuel, Houdier Stephan, Hall Sam, . (2011). Soluble, light-absorbing species in snow at Barrow, Alaska
. J. Geophys. Res., 116, D00R05–.
Abstract: As part of the international multidisciplinary Ocean – Atmosphere – Sea Ice – Snowpack (OASIS) program we analyzed more than 500 terrestrial (melted) snow samples near Barrow, AK between February and April 2009 for light absorption, as well as H2O2 and inorganic anion concentrations. For light absorption in the photochemically active region (300–450 nm) of surface snows, H2O2 and NO3- make minor contributions (combined < 9% typically), while HUmic LIke Substances (HULIS) and unknown chromophores each account for approximately half of the total absorption. We have identified four main sources for our residual chromophores (i.e., species other than H2O2 or NO3-): (1) vegetation and organic debris impact mostly the lowest 20 cm of the snowpack, (2) marine inputs, which are identified by high Cl- and SO42- contents, (3) deposition of diamond dust to surface snow, and (4) gas-phase exchange between the atmosphere and surface snow layers. The snow surfaces, and accompanying chromophore concentrations, are strongly modulated by winds and snowfall at Barrow. However, even with these physical controls on light absorption, we see an overall decline of light absorption in near-surface snow during the 7 weeks of our campaign, likely due to photo-bleaching of chromophores. While HULIS and unknown chromophores dominate light absorption by soluble species in Barrow snow, we know little about the photochemistry of these species, and thus we as a community are probably overlooking many snowpack photochemical reactions.
Keywords: HULIS, OASIS, chromophores, light absorption, snow pack, 0317 Atmospheric Composition and Structure: Chemical kinetic and photochemical properties, 0322 Atmospheric Composition and Structure: Constituent sources and sinks, 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry, 0736 Cryosphere: Snow (1827, 1863),
Programme: 1017
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France J L, Reay H J, King M D, Voisin D, Jacobi H W, Domine F, Beine H, Anastasio C, MacArthur A, Lee-Taylor J,. (2012). Hydroxyl radical and NOx production rates, black carbon concentrations and light-absorbing impurities in snow from field measurements of light penetration and nadir reflectivity of onshore and offshore coastal Alaskan snow. J. Geophys. Res., 117, D00R12 ST -.
Abstract: Photolytic production rates of NO, NO2 and OH radicals in snow and the total absorption spectrum due to impurities in snowpack have been calculated for the Ocean-Atmosphere-Sea-Ice-Snowpack (OASIS) campaign during Spring 2009 at Barrow, Alaska. The photolytic production rate and snowpack absorption cross-sections were calculated from measurements of snowpack stratigraphy, light penetration depths (e-folding depths), nadir reflectivity (350–700 nm) and UV broadband atmospheric radiation. Maximum NOx fluxes calculated during the campaign owing to combined nitrate and nitrite photolysis were calculated as 72 nmol m-2 h-1 for the inland snowpack and 44 nmol m-2 h-1 for the snow on sea-ice and snowpack around the Barrow Arctic Research Center (BARC). Depth-integrated photochemical production rates of OH radicals were calculated giving maximum OH depth-integrated production rates of ~160 nmol m-2 h-1 for the inland snowpack and ~110–120 nmol m-2 h-1 for the snow around BARC and snow on sea-ice. Light penetration (e-folding) depths at a wavelength of 400 nm measured for snowpack in the vicinity of Barrow and snow on sea-ice are ~9 cm and 14 cm for snow 15 km inland. Fitting scaled HULIS (HUmic-LIke Substances) and black carbon absorption cross-sections to the determined snow impurity absorption cross-sections show a “humic-like” component to snowpack absorption, with typical concentrations of 1.2–1.5 μgC g-1. Estimates of black carbon concentrations for the four snowpacks are ~40 to 70 ng g-1 for the terrestrial Arctic snowpacks and ~90 ng g-1 for snow on sea-ice.
Keywords: Barrow OH black carbon e-folding depth nitrate photochemistry 0736 Cryosphere: Snow (1827, 1863) 0770 Cryosphere: Properties 0798 Cryosphere: Modeling (1952, 4316),
Programme: 1017
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Domine Florent, Bock Josu, Morin Samuel, Giraud Grald, . (2011). Linking the effective thermal conductivity of snow to its shear strength and density
. J. Geophys. Res., 116(F4), F04027–.
Abstract: The effective thermal conductivity of snow, keff, is a crucial climatic and environmental variable. Here, we test the intuition that keff is linked to microstructural and mechanical properties by attempting to relate keff to density ρsnow, and to shear strength σ measured with a handheld shear vane. We performed 106 combined measurements of keff, ρsnow and σ in the Alps, Svalbard, Arctic Alaska, and near the North Pole, covering essentially all snow types. We find a good correlation between keff and ρsnow which is not significantly different from that of Sturm et al. (1997). The correlation between keff and a combination of σ and ρsnow is stronger than with density alone. We propose an equation linking keff, (W m-1 K-1) ρsnow (kg m-3) and σ (Pa): keff = 7.114 10-5 ρsnow σ0.333 + 2.367 10-2. This equation places constraints on the calculation of keff, ρsnow and σ in avalanche warning models where σ is a key variable. For our samples, we calculate σ from measured values of keff and ρsnow using our equation and compare the value to that predicted by the French MEPRA avalanche warning model, which uses density and grain type as input data. MEPRA and the prediction of σ based on keff and ρsnow agree within 8%. MEPRA agrees with observations within 11%. Calculating σ from density only yields values 55% lower than measured, showing the interest of using additional data to predict σ.
Keywords: avalanche, shear strength, snow, thermal conductivity, 0736 Cryosphere: Snow (1827, 1863), 0742 Cryosphere: Avalanches (4302), 0770 Cryosphere: Properties, 0776 Cryosphere: Glaciology (1621, 1827, 1863),
Programme: 1017
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Domine F, Gallet Jean-Charles, Bock Josué, Morin Samuel,. (2012). Structure, specific surface area and thermal conductivity of the snowpack around Barrow, Alaska. J. Geophys. Res., 117, D00R14 ST -.
Abstract: The structure of the snowpack near Barrow was studied in March–April 2009. Vertical profiles of density, specific surface area (SSA) and thermal conductivity were measured on tundra, lakes and landfast ice. The average thickness was 41 cm on tundra and 21 cm on fast ice. Layers observed were diamond dust or recent wind drifts on top, overlaying wind slabs, occasional faceted crystals and melt-freeze crusts, and basal depth hoar layers. The top layer had a SSA between 45 and 224 m2 kg-1. All layers at Barrow had SSAs higher than at many other places because of the geographical and climatic characteristics of Barrow. In particular, a given snow layer was remobilized several times by frequent winds, which resulted in SSA increases each time. The average snow area index (SAI, the dimensionless vertically integrated SSA) on tundra was 3260, higher than in the Canadian High Arctic or in the Alaskan taiga. This high SAI, combined with low snow temperatures, imply that the Barrow snowpack efficiently traps persistent organic pollutants, as illustrated with simple calculations for PCB 28 and PCB 180. The average thermal conductivity was 0.21 Wm-1 K-1, and the average thermal resistance on tundra was 3.25 m2 K W-1. This low value partly explains why the snow-ground interface was cold, around -19°C. The high SAI and low thermal resistance values illustrate the interplay between climate, snow physical properties, and their potential impact on atmospheric chemistry, and the need to describe these relationships in models of polar climate and atmospheric chemistry, especially in a climate change context.
Keywords: Arctic atmospheric chemistry climate contaminants polar snow 0475 Biogeosciences: Permafrost, cryosphere, and high-latitude processes (0702, 0716) 0718 Cryosphere: Tundra (9315) 0736 Cryosphere: Snow (1827, 1863) 0750 Cryosphere: Sea ice (4540) 0792 Cryosphere: Contaminants (0432),
Programme: 1017
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Beine Harry, Anastasio Cort, Domine Florent, Douglas Thomas, Barret Manuel, France James, King Martin, Hall Sam, Ullmann Kirk, . (2012). Soluble chromophores in marine snow, seawater, sea ice and frost flowers near Barrow, Alaska
. J. Geophys. Res., 117, D00R15–.
Abstract: We measured light absorption in 42 marine snow, sea ice, seawater, brine, and frost flower samples collected during the OASIS field campaign between February 27 and April 15, 2009. Samples represented multiple sites between landfast ice and open pack ice in coastal areas approximately 5 km west of Barrow, Alaska. The chromophores that are most commonly measured in snow, H2O2, NO3-, and NO2-, on average account for less than 1% of sunlight absorption in our samples. Instead, light absorption is dominated by unidentified “residual” species, likely organic compounds. Light absorption coefficients for the frost flowers on first-year sea ice are, on average, 40 times larger than values for terrestrial snow samples at Barrow, suggesting very large rates of photochemical reactions in frost flowers. For our marine samples the calculated rates of sunlight absorption and OH production from known chromophores are (0.1–1.4) 1014 (photons cm-3 s-1) and (5–70) 10-12 (mol L-1 s-1), respectively. Our residual spectra are similar to spectra of marine chromophoric dissolved organic matter (CDOM), suggesting that CDOM is the dominant chromophore in our samples. Based on our light absorption measurements we estimate dissolved organic carbon (DOC) concentrations in Barrow seawater and frost flowers as approximately 130 and 360 μM C, respectively. We expect that CDOM is a major source of OH in our marine samples, and it is likely to have other significant photochemistry as well.
Keywords: OASIS, chromophores, colored dissolved organic matter (CDOM), frost flowers, light absorption, marine, 0317 Atmospheric Composition and Structure: Chemical kinetic and photochemical properties, 0322 Atmospheric Composition and Structure: Constituent sources and sinks, 0736 Cryosphere: Snow (1827, 1863), 0750 Cryosphere: Sea ice (4540), 4807 Oceanography: Biological and Chemical: Chemical speciation and complexation,
Programme: 1017
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H. W. Jacobi, D. Voisin, J. L. Jaffrezo, J. Cozic, T. A. Douglas. (2012). Chemical composition of the snowpack during the OASIS spring campaign 2009 at Barrow, Alaska (Vol. 117).
Abstract: The chemical composition of the seasonal snowpack was determined close to Barrow, an Arctic coastal location in northern Alaska. One hundred and twelve samples of different snow types including fresh snow, surface hoar, diamond dust, blowing snow, rounded snow grains, and depth hoar were collected and analyzed for major sea salt components, bromide, and nitrate. Sodium, chloride, sulfate, and potassium are mainly introduced into the snowpack by the deposition of sea salt, while magnesium and calcium result from a combination of sea salt and dust. Sulfate was strongly depleted in most samples compared to other sea salt components. This is attributed to the precipitation of mirabilite in newly formed sea ice and frost flowers that leads to an efficient fractionation of sulfate. Uptake of volatile but soluble species from the gas phase also contributed to the observed chloride, sulfate, and nitrate in the snow. However, for chloride and sulfate the input from the marine sources was overwhelming and the uptake from the gas phase was only visible in the samples with low concentrations like fresh snow, diamond dust, and surface hoar. Nitrate concentrations in the snowpack were less variable and for aged snow nitrate was related to the specific surface area of the snow indicating the adsorption of nitric acid can be an important nitrate source in the aged snow. Bromide was also introduced into the snowpack from marine sources, but due to its high reactivity it was partly transferred back to the atmosphere in the form of reactive species. The result of these processes was evident in bromide concentrations, which were both enriched and depleted at the snowpack surface while deeper layers were mostly depleted. Blowing snow also exhibited a depleted bromide composition. For all compounds except nitrate, many depth hoar samples exhibited the greatest concentrations, probably as a result of higher input earlier in the season as well as increases due to the sublimation of water during the metamorphism of the snow.
Keywords: Alaska Arctic Barrow Chemistry Snow
Programme: 1017
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Hans-Werner Jacobi, Jörg Kleffmann, Guillermo Villena, Peter Wiesen, Martin King, James France, Cort Anastasio, Ralf Staebler. (2014). Role of Nitrite in the Photochemical Formation of Radicals in the Snow (Vol. 48).
Abstract: Photochemical reactions in snow can have an important impact on the composition of the atmosphere over snow-covered areas as well as on the composition of the snow itself. One of the major photochemical processes is the photolysis of nitrate leading to the formation of volatile nitrogen compounds. We report nitrite concentrations determined together with nitrate and hydrogen peroxide in surface snow collected at the coastal site of Barrow, Alaska. The results demonstrate that nitrite likely plays a significant role as a precursor for reactive hydroxyl radicals as well as volatile nitrogen oxides in the snow. Pollution events leading to high concentrations of nitrous acid in the atmosphere contributed to an observed increase in nitrite in the surface snow layer during nighttime. Observed daytime nitrite concentrations are much higher than values predicted from steady-state concentrations based on photolysis of nitrate and nitrite indicating that we do not fully understand the production of nitrite and nitrous acid in snow. The discrepancy between observed and expected nitrite concentrations is probably due to a combination of factors, including an incomplete understanding of the reactive environment and chemical processes in snow, and a lack of consideration of the vertical structure of snow.
Programme: 1017
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Lev Vinnik, Elena Kozlovskaya, Sergey Oreshin, Grigoriy Kosarev, Katerina Piiponen, Hanna Silvennoinen. (2016). The lithosphere, LAB, LVZ and Lehmann discontinuity under central Fennoscandia from receiver functions (Vol. 667).
Abstract: P- and S-wave velocity profiles (Vp and Vs) from the Earth's surface to a depth of 300km are obtained by simultaneous inversion of P- and S-wave receiver functions for the temporary POLENET/LAPNET array in northern Finland and 5 permanent stations in southern Finland. The obtained Vp/Vs velocity ratio in the uppermost mantle is anomalously low (1.65–1.70 versus the standard 1.8). This ratio can be explained by a high (~30%) fraction of orthopyroxene in the depleted upper mantle. An increase of ~4% in the Vs values is detected at a depth of 110–130km. Under southern Finland the high-velocity mantle keel may extend beyond the depth of 300km, but under northern Finland we detect a low-Vs zone (LVZ) with the top at a depth of 160km. This depth corresponds to the intersection of the geotherm with the wet solidus of peridotite at a temperature near ~1100°C, and suggests partial melting as an explanation for the origin of the LVZ. The bottom of the LVZ (the Lehmann discontinuity) is found at a depth of 240km. The fast direction of seismic azimuthal anisotropy beneath northern Finland in the depth interval from 200–240km to 320km is parallel to the current APM direction (60°) but in the interval from 160km to 200–240km the fast direction (150°) appears to be normal to the APM direction (Vinnik et al., 2014). The present study indicates that the fast direction of 150° confines to the LVZ where the flow in the direction normal to the APM direction is unlikely. More likely, the flow direction is parallel to the APM direction and normal to the fast direction of anisotropy, as suggested by experiments with sheared peridotite-type rocks containing melt.
Keywords: LAB Lehmann discontinuity Low-velocity zone Partial melting Receiver functions Seismic anisotropy
Programme: 1021
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Olga Usoltseva, Elena Kozlovskaya. (2016). Studying local earthquakes in the area Baltic-Bothnia Megashear using the data of the POLENET/LAPNET temporary array (Vol. 7).
Abstract: Earthquakes in areas within continental plates are still not completely understood, and progress on understanding intraplate seismicity is slow due to a short history of instrumental seismology and sparse regional seismic networks in seismically non-active areas. However, knowledge about position and depth of seismogenic structures in such areas is necessary in order to estimate seismic hazard for such critical facilities such as nuclear power plants and nuclear waste deposits. In the present paper we address the problem of seismicity in the intraplate area of northern Fennoscandia using the information on local events recorded by the POLENET/LAPNET (Polar Earth Observing Network) temporary seismic array during the International Polar Year 2007–2009. We relocate the seismic events using the program HYPOELLIPS (a computer program for determining local earthquake hypocentral parameters) and grid search method. We use the first arrivals of P waves of local events in order to calculate a 3-D tomographic P wave velocity model of the uppermost crust (down to 20 km) for a selected region inside the study area and show that the velocity heterogeneities in the upper crust correlate well with known tectonic units. We compare the position of the velocity heterogeneities with the seismogenic structures delineated by epicentres of relocated events and demonstrate that these structures generally do not correlate with the crustal units formed as a result of crustal evolution in the Archaean and Palaeoproterozoic. On the contrary, they correlate well with the postglacial faults located in the area of the Baltic-Bothnia Megashear (BBMS). Hypocentres of local events have depths down to 30 km. We also obtain the focal mechanism of a selected event with good data quality. The focal mechanism is of oblique type with strike-slip prevailing. Our results demonstrate that the Baltic-Bothnia Megashear is an important large-scale, reactivated tectonic structure that has to be taken into account when estimating seismic hazard in northern Fennoscandia.
Programme: 1021
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Lev Vinnik, Sergey Oreshin, Larissa Makeyeva, Dmitriy Peregoudov, Elena Kozlovskaya, Elena Kozlovskaya, Helle Pedersen, Jaroslava Plomerova, Ulrich Achauer, Eduard Kissling, Irina Sanina, Teppo Jämsen, Hanna Silvennoinen, Catherine Pequegnat, Riitta Hurskainen, Robert Guiguet, Helmut Hausmann, Petr Jedlicka, Igor Aleshin, Ekaterina Bourova, Reynir Bodvarsson, Evald Brückl, Tuna Eken, Pekka Heikkinen, Gregory Houseman, Helge Johnsen, Elena Kremenetskaya, Kari Komminaho, Helena Munzarova, Roland Roberts, Bohuslav Ruzek, Hossein Shomali, Johannes Schweitzer, Artem Shaumyan, Ludek Vecsey, Sergei Volosov. (2014). Anisotropic lithosphere under the Fennoscandian shield from P receiver functions and SKS waveforms of the POLENET/LAPNET array (Vol. 628).
Abstract: Seismic azimuthal anisotropy is the key evidence of the past and present strains in the upper mantle. The standard analysis of shear-wave splitting with the SKS techniques is useful in mapping lateral variations but it is insensitive to depth of anisotropy and to variations of anisotropy with depth. To retrieve the depth localized anisotropy under the Fennoscandian shield, we inverted P-wave receiver functions of the POLENET/LAPNET array in northern Finland jointly with SKS recordings. Shear-wave anisotropy of ~2.5% with the fast direction of 40°–60° in a depth range from the Moho to ~110km is a robust result of the inversion. The obtained direction is nearly normal to the azimuth of the maximum horizontal compressional stress in the lithosphere, but a recent origin of this anisotropy is in doubt. This anisotropy may be frozen since the Precambrian, but it shows no clear relation with the trends of the Precambrian tectonics. The upper anisotropic layer accounts for ~40% of shear-wave splitting in SKS, and to explain the rest another anisotropic layer is required. The top of the second layer with a practically similar fast direction is found at a depth of 200–240km. This direction is close to the current APM direction of the lithosphere with implication that the inferred anisotropy may be related with the current plate motion, and the anisotropic layer belongs to the asthenosphere. The bottom of this layer is uncertain, but it is at least 320km deep. In a depth range from 160km to 200–240km the fast anisotropy direction is 110–150°. Origin of this direction is unclear.
Keywords: Asthenosphere Lithosphere Mantle flow Receiver functions Seismic anisotropy Shear-wave splitting
Programme: 1021
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